How about High Voltage fuse for Motor protection?
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The SIBA HHM fuse-links all requirements according IEC
60644 “Specification for high-voltage fuse-links for motor
circuit application”.
The special characteristic allows a full short circuit
protection for the motor circuit components as well as
a withstand capability for starting inrush currents and
cyclic current impulses.
Application
guideline:
The suitable rated current of the fuse-link is mainly
determined by two important parameters:
·the inrush-current during the run-up period of the motor
due to high magnetizing-currents
·to create less heating in the enclosure
For general, the inrush current can be calculated as five
to six times rated current of the motor.
For practical use the run-up time of different motor types
are separated into three main categories:
Table 1:run-up times
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example
of motor type |
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| pump-motor |
| mill-motor |
| fan-motor |
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To avoid any aging due to frequent switching-operations
following derating-coefficients have to taken into account:
Table 2:derating-coefficients
Note: Two immediate successive starts are admissible.
Selection-procedure:
· determine the inrush-current (individually
given, or multiply the normal operating of the motor
by 6) and divide it by the corresponding derating-coefficient
of table 2,considering the quantity of starts per
hour
· transfer this value to the X-axis of the time
current characteristic of the fuse-link
· mark the crossing-point of these X-and Y-valuse
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The time current curve of the fuse-link, which is directly
placed on the right side next to the marked point, reflects
the correct rated current of the fuse-link have to be
chosen.This rated current of the fuse-link must at least
1.3 times of the normal operating current of the motor.
In other cases the next higher rated current has to be
taken.
The above-mentioned procedure is valid for direct-staring
motors as well as for assisted-starting. In this case
the calculated inrush current is decreased and a smaller
rated current of the fuse-link could be chosen as in case
of direct-starting.
For such applications an inadmissible temperature increase
must be avoided by a rated current of the fuse-link higher
or equal to 1.3 times normal operating current of the
motor.
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